This application claims the priority of German Patent Document No. 197 25 008.4, filed on Jun. 13, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for the operation of a methanol reforming apparatus using a methanol reforming catalyst that loses its activity in the reforming reaction, and which comprises interrupting the reforming reaction operation at given times for catalyst reactivation phases.
Methods for reforming methanol are variously known and serve, for example, for the production of hydrogen for the fuel cells of a fuel-cell-operated motor vehicle by means of water vapor reforming of fluid methanol carried with it. A catalytically active Cu/ZnO material on an aluminum oxide support is suitable, for example, as catalyst material. Other usable catalyst compositions are described, for example, in patent applications DE 35 31 757 A1 and EP 0 201 070 A1. Usually the catalyst material is loaded in the form of pellets in bulk into the reforming reaction chamber of the methanol reforming reactor in question.
It is a known fact of current methanol reforming catalysts that, during the reforming reaction process they show a loss of their specific activity. This is especially true in the case of high load operation, such as is desirable in mobile applications, in which use an especially compact construction of the reactor is sought for reasons of space and weight. The reactor is then operated at a corresponding high load so as to achieve the required conversion performance. Frequent replacement of the catalyst material is difficult considering the mobility and service expectations of automobile users.
Various methods are already known for sustaining a high catalytic activity and achieving a long life of the methanol reforming catalyst. Thus, in patent application JP 4-141234 (A) a special formula of various metal oxides is given for the purpose of obtaining a catalyst with a long life and high activity and selectivity.
In patent application JP 63-310703 (A), before the reforming reaction operation is started, the catalyst material is subjected in the reforming reaction chamber of a methanol reforming reactor to a reduction reaction resulting in a shrinkage of the volume of the catalyst. A spring-loaded, movable cover plate holds the catalyst material, charged into the reactor, in a tightly packed form. The reduction reaction is a necessary procedure for the operation of a copper catalyst. The shrinkage that occurs is definitely less than the shrinkage that occurs during normal reforming operations.
In patent application JP 63-315501 (A) the placement of an air chamber between a burner and a reforming reaction chamber is proposed, through which air can be fed in a controlled manner in order to keep the catalyst temperature at a given level.
In a method disclosed in patent application DE 33 14 131 A1, to extend the life of the methanol reforming catalyst the methanol is freed of any chlorine compounds that might be contained in it, before it is brought in contact with the catalyst.
In patent application DE 1 246 688 a method of the kind referred to above is described, in which a methanol-water mixture for the methanol reforming is passed over a nickel catalyst and a zinc-copper catalyst. This reforming operation is periodically interrupted for catalyst treatment phases which consist of a catalyst regeneration phase and, optionally, a subsequent nickel catalyst reactivation phase. The regeneration phase consists in passing a gas which contains free oxygen through the reactor at an elevated temperature of preferably 150.degree. C. to 450.degree. C. The optional nickel catalyst reactivation phase consists in passing a gas containing free hydrogen through the catalyst system at an elevated temperature.